IgA nephropathy is a type of chronic glomerulonephritis characterized by IgA deposition dominantly in the glomerular mesangium area of the kidney. IgA nephropathy cases account for the majority of chronic glomerulonephritis cases in Japan, and as a single renal disease, are largest in number. Of such IgA nephropathy cases, 15 to 30% having a poor prognosis progress into renal failure, and there is no radical therapy because the etiology of IgA nephropathy is still unknown. The definitive diagnosis of IgA nephropathy is a heavy burden on patients because it is based on a method involving biopsy in which a portion of the kidney is excised and immunologically stained to confirm IgA immune complex deposition in the mesangium. Accordingly, desired is a method for detecting presumed IgA nephropathy with a high accuracy, the method being simply and quickly practicable without physical burden on subjects before renal biopsy.
It is known that, regarding IgA, which is categorized into two types IgA1 and IgA2, IgA1 is produced in the upper gastrointestinal tract, the respiratory tract and the tonsil while IgA2 is produced in the lower gastrointestinal tract. Since IgA nephropathy is associated with IgA1 deposition in the kidney, tonsillectomy as a therapy for IgA nephropathy patients has been performed in recent years.
Non Patent Literature 1 reports that three years after tonsillectomy was performed in 16 IgA nephropathy patients, remission of proteinuria was observed in 56.3% of them. Non Patent Literature 2 also reports that tonsillectomy was performed in 24 IgA nephropathy patients and that remission of proteinuria was observed in 41.7% of them six months later and in 50% of them two years later. Further, Non Patent Literature 3 reports that combination of tonsillectomy and steroid pulse therapy produced remission of both of proteinuria and hematuria in about 60% of IgA nephropathy patients.
However, tonsillectomy is not effective for about 40% of IgA nephropathy patients, and whether or not tonsillectomy is effective for each individual patient cannot be presumed beforehand. Since tonsillectomy operation requires general anesthesia and thus is heavy physical burden on the patients, desired is the establishment of a method for screening for, with a high accuracy, a patient for whom tonsillectomy is effective.